The present invention relates to a clamping device for attachment to two elements that are movable relative to one another in order to clamp the two elements in any desired relative position. The clamping device is particularly intended for use with an adjustable vehicle steering wheel to enable it to be locked at any rake angle that is comfortable for the vehicle driver.
It is known to provide a universal joint in a steering column to allow the upper part of the steering column to be pivoted relative to its lower part, thereby allowing the rake or tilt of the steering wheel to be adjusted for driver comfort. The casing in which the two parts of the steering column are journalled is formed in two parts that can pivot relative to one another and that are clamped firmly in one position after the steering wheel has been moved into a comfortable position. The clamping device of the present invention is intended for such an application though it may be used in other situations where it is desired to clamp relatively movable elements, in order to maintain them a fixed distance apart.
The conventional manner of locking a tilt steering wheel is to provide a U-shaped bracket that hangs beneath the vehicle dashboard or is otherwise attached to the vehicle body, the two arms of the bracket straddling the upper part of the steering column. A clamping device on the bracket serves to prevent the steering column from moving inside the bracket.
Various clamping devices are known, for example from U.S. Pat. Nos. 5,265,492, 5,199,319 and EP-A-0.368.700 that use a handle pivoted on the bracket. Rotation of the handle in one direction locks the steering wheel while rotation of the handle in the opposite direction releases the steering wheel to allow it to be moved to a new position. Because a high clamping force is needed to prevent the steering column from tilting after it has been set in its desired position, it is necessary to use a long and obtrusive handle.
U.S. Pat. No. 4,240,305 uses a screw on a split collar to grip the steering column. Here, considerable effort is required to tighten the screw in order to grip the steering wheel sufficiently firmly to prevent it from moving inadvertently. Releasing the screw to readjust the position of the steering wheel after a time can prove even more difficult. SUMMARY OF THE INVENTION
With a view to mitigating the foregoing disadvantages, there is provided in accordance with the present invention, a clamping device for attachment to two elements in order to clamp the two elements in any desired relative position, the clamping device comprising a rod for attachment to one of the elements, a collar for attachment to the other element and having an aperture through which the rod passes with clearance and a locking member mounted at a position along the axis of the rod spaced from the aperture and adjustable manually to apply a force between the collar and the rod in a direction to cause the collar to tilt relative to the rod, so as to jam the rod within the aperture.
The forces applied to a steering wheel during use act predominantly downwards and it is these forces that the clamping device must withstand to prevent the position of the steering wheel changing unintentionally during normal steering of the vehicle. In the present invention, the locking member is not required to apply a sufficiently high frictional force between the collar and the rod to prevent the rod from sliding inside the collar when a downward force is applied to the steering wheel. Instead the locking member acts to tilt the collar, until the rod is jammed in the aperture by making contact with the collar on opposite sides of the upper and lower edges of the aperture.
If the rod should try to move relative to the aperture in the direction corresponding to a downward force being applied to the steering wheel, then the friction between the collar and the rod will act in the direction to make the collar tilt still further and grip the rod even more tightly. The frictional force created by the locking member need therefore only be sufficiently high to resist the lesser forces acting upwards on the steering wheel.
The locking member is preferably a screw threaded into the collar at right angles to the rod and having a knob that may be manually gripped.
When the locking member is released, if the rod is to be allowed to move freely relative to the collar, then it is necessary to ensure that the collar will return to a position in which the aperture and the rod are coaxial.
In a preferred embodiment of the invention, a sleeve is slidably mounted on the rod and is urged by a spring towards the collar, the collar and the sleeve having complementary conically tapered axial end surfaces that interact with one another under the action of the spring to align the aperture in the collar with the axis of the rod.
Conveniently, the rod, the spring and the collar are formed as a preassembled unit, the rod being fitted with a stop, such as a circlip, to prevent the collar from sliding off the rod.
The spring may conveniently comprise a helical spring acting between a shoulder on the sleeve and a pivot pin by means of which the rod is attached to one of the two elements. In this case, the spring assists in supporting the weight of the steering wheel and column when the clamping device is released and returns the steering column to an upper position.
The spring urging the sleeve towards the collar may additionally or alternatively comprise spring clips secured to the collar and resiliently engaging a surface of the sleeve.